Empowered Patient is a regular feature from CNN Medical News correspondent Elizabeth Cohen that helps put you in the driver's seat when it comes to health care.

ATLANTA, Georgia (CNN) -- After Marci Smith was told she had a malignant brain tumor, she had surgery and then made an appointment with an oncologist to receive chemotherapy and radiation.

Fewer people are having bypass surgeries -- 249,000 in 2004 compared with 314,000 in 2000, the CDC says.

But Smith never kept that appointment.

A nagging voice inside her head told her to get a second opinion. In the end, that voice is the reason Smith is getting the right treatment.

The first doctor's pathologist said Smith had a type of tumor called a sarcoma. But a second opinion -- and a third and a fourth -- said she had a glioblastoma, another type of brain tumor that requires much different treatment. Further pathology tests confirmed the glioblastoma.

"You always need to ask, 'Are you sure this is what it is?' " says Smith, who's receiving treatment for her glioblastoma near her home in Tennessee.

While it's important to get second opinions for various treatments, doctors say there are certain procedures where it's especially crucial: when the diagnosis is tricky, the procedure is risky or has permanent consequences, or when there are less-invasive alternatives. Interactive quiz: How much do you know about these procedures? »

Here are five diagnoses in which patients should seek a second opinion, according to experts.

1. Heart bypass surgery

"Anytime you're considering a procedure that has a risk of dying, stroke and severe infection, you should get a second opinion," says Dr. Richard Stein, director of preventive cardiology at Beth Israel Medical Center in New York.

Stein says alternatives such as angioplasty or medications with exercise are less risky and may be better for some patients.

He says these alternatives are part of the reason fewer people are having bypass surgeries -- 249,000 had bypass surgery in 2004 compared with 314,000 in 2000, according to the Centers for Disease Control and Prevention.

2. Hysterectomy

Sometimes doctors recommend surgical removal of the uterus for bleeding or pelvic pain when the uterus isn't the problem at all.

"Almost on a monthly basis, I will see a patient whose doctor told them to get a hysterectomy, and it turns out they have myofascial pain," says Dr. Howard Sharp, vice chair of clinical affairs in the Department of Obstetrics and Gynecology at the University of Utah School of Medicine.

Myofascial pain is a type of musculoskeletal pain that can be treated with icing, stretching and anesthesia injections.

Even when the problem is in the uterus, there are alternatives to a hysterectomy. "There are lots of less-invasive options these days," says Dr. Jessica Bienstock, associate professor of maternal-fetal medicine at Johns Hopkins Medical Institutions.

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For example, she says hormone treatments might be the answer to pelvic pain, and embolization -- cutting off the blood supply to the fibroids -- might be an option for uterine fibroids.

3. Pregnancy termination for fetal abnormality

Sometimes parents choose to terminate a pregnancy when the fetus has a severe abnormality -- but they should make sure they have the right diagnosis before they do it.

"I can't tell you how many times we get referrals for one diagnosis, and it actually turns out to be something different," Bienstock says.

For example, sometimes a fetus might be diagnosed with having a congenital cystic adenomatoid malformation -- an abnormal formation in the lungs -- but actually turns out to have a diaphragmatic hernia. Parents might make different decisions based on these diagnoses, Bienstock says.

4. Surgery for varicose veins

There are so many different treatment options for varicose veins, it's best to get a second opinion, according to Dr. Julie Fleishlag, chair of the department of surgery at Johns Hopkins.

Exercise, use of stockings, injections, surgery and laser treatments are all options, she says.

"Go to someone who does all these types of interventions," she suggests, since a doctor who performs only one might be biased. "If you get the wrong procedure, it won't last long."

5. Treatments for brain tumors

As Smith learned, the wrong brain tumor diagnosis could lead to the wrong treatment. The diagnosis depends largely on the pathologist reading a slide -- and mistakes can happen.

Sometimes brain tumors are diagnosed when they aren't even tumors at all, says Evan Falchuk, president of Best Doctors, a company that helps patients get second opinions. "You may not need brain surgery because what they told you was a tumor was in fact an inflammatory disease, treatable with medicines," Falchuk says.

For Smith, it all came down to that voice in her head that told her she needed a second opinion. But it wasn't easy. "People turn over their authority to the doctor the minute they get sick," she says. "You want help so desperately you say, 'Whatever you want to do, let's do it.' "

Even if it's hard, patients need to question their doctors, says Stein, the cardiologist at Beth Israel. "We need to give up the Dr. Marcus Welby model of medical care," he says. "You're the consumer who's taking the risk. As you would for any financial decisions, you should get a second opinion."E-mail to a friend